Liquid crystal displays (LCDs) are non-emissive displays that utilize a separate backlight unit and red, green and blue color filters for pixels to display a color image on a screen. The red, green and blue color filters respectively separate white light emitted from the backlight unit into red, green and blue lights. The range of colors that can be displayed by an LCD device is called color gamut.
LCD backlight systems typically include a film stack containing a reflector plate or film, a light guide (for example, a light guide plate or light guide film) containing extraction features, a diffusing sheet, light redirecting films (for example, prism films, lenticular films and/or other brightness enhancement films) and/or a reflective polarizer. Traditionally, LCDs have utilized white light-emitting diodes (LEDs) consisting of a blue LED die combined with a yellow YAG phosphor. Mobile/handheld devices are typically edge-lit and contain a light guide to uniformly distribute light over the display area. The “white” light is then diffused out of the light guide using a diffuser sheet. Recently, however, LCDs having improved color gamut been developed. In these LCDs, white LEDs are replaced with blue LEDs and the diffuser sheet is replaced with a downconversion film element that actively converts color. The downconversion sheet may comprise, for example, red and green quantum dots, phosphors, fluorescing dyes and the like. By simply replacing the bottom diffuser sheet in a typical LCD backlight with a quantum dot film element, the achieved color gamut can be increased dramatically (for example, by 50%).
One issue associated with backlight systems containing quantum dot film elements or other downconversion film elements is color non-uniformities near the boundaries of the backlight (that is, at the edges of the viewable area of the display). Typically, this non-uniformity manifests itself as a blue glow at the edge of the viewable area of the display. This glow is commonly thought to be the result of blue light leakage out of the edge of the backlight system.